Purifying zinc



March l2, 1935. P. Mel.. GINDER Er AL 11,994,357

PURIFYING ZINC Filed May 26, 1933 2 Sheets-Sheet l INVENTORS ATTORNEYS gid' w @Imam March l2, 1935. P, Mel.. GINDER Er AL 1,994,357

PURIFYING ZINC Filed May 26, 1933 2 Sheets-Sheet 2 INVENTORS C? cz. si.

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ATTORNEYS Patented -Mar. 12., 1935 I UNITED STATES PATENT oFElcE PURIFYING ZINC Philip McLean Ginder, Willis McGcrald Peirce, and Robert Kerr Waring, Palmerton, Pa., assignors to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application May as, 193s, serial No. 672.998 2 claims. (o1. z5-28)' This invention relates to purifying zinc metal Figs. 2, 3 and 4 are explanatory sectional views by distillation, and has for its object the provion the section lines 2--2, 3 3 and 1 -4, respecsion of an improved method of and apparatus for tively, of Fig. 1, and producing purified zinc vapor from zinc metal Fig. 5 is a detailed sectional view on the section 5 contaminated with both lead and cadmium, or line 5-5 of Fig. 4.

other metallic impurities of higher and lower Referring to Fig. 1 of the drawings, there is boiling points than zinc. Throughout this specilshown an upright furnace structure having a cation and the appended claims, lead and cadheating chamber or laboratory 11 provided with mium are taken as .representative of metal imburner openings 12 and an outlet (not shown in l0 purities of higher and lower boiling points, rethe drawings) near the top thereof for the ex- 10 spectively, than zinc, and it is therefore to be haust heating gases. It will, of course, be underunderstood that specific mention of lead and stood that any other appropriate means of heatcadmium in the specification and claims is illusing may be used in lieu of the burners and hot trative and not restrictive. gases of combustion indicated in the drawings.

In our co-pending application for Letters Patent The lower portion of a cadmium-eliminating l5 of the United States, Ser. No. 620,634, filed July rectifying column (hereinafter designated Acad- 2, 1932, we have disclosed a method of and apmium column) is built within the heating champaratus for removing cadmium and the like from ber 11. 'I'his lower portion of the column is built zinc metal by fractional distillation in a rectifying up of rectangular trays or pots 13 of silicon carcolumn. In another copending application for bide or equivalent refractory material of good 20 Letters Patent of the United States, Ser. No. heat conductivity. The top and bottom edges 668,314, iiled April 28, 1933, we have disclosed of the trays are bevelled as at 14 so that they may a novel and advantageous combination of our be stacked one above the other to form an upmethod of cadmium elimination with the method right or vertical column. The joints between the of eliminating lead from zinc metal by the rectrays are made zinc-vapor-tight by an appropri- 25 tifying action of a reflux column described in the ate cement, such as a cement of silicon carbide copending application of Messrs. Holstein and with a. small amount' of clay. Each tray 13 has Ginder, Ser. No. 540,566, filed May 28, 1931. Our a V-shaped peripheral trough or channel 15 for present invention involves a further novel and holding molten metal. This trough is formed beadvantageous combination of these methods of tween the outer wall of the tray and an inner n- 30 removing lead and cadmium from impure zinc clined wall16 of the bottom 17 of the tray. Each metal by fractional distillation in a rectifying tray is an integrally molded article. The bottom Y column, and is characterized by rst subjecting 17 has an opening 18 approximate one end therethe impure molten zinc metal to a rectification of, and the upper edge of the opening has a rib 19 235 treatment for the removal of cadmium and then for retaining a shallow layer of molten metal on subjecting the so-treated impure molten zinc the top surface of the bottom member 17 (see metal to a second rectification treatment for the Fig. 3).

removal of lead, whereby purified zinc vapor is The trays 13 are stacked in staggered relationobtained. Thus, the present invention involves ship with respect to the openings 18 so that the 10 subjecting zinc metal contaminated with lead and bottoms thereof form a column of superposed and 40 cadmium to two successive rectification treatvertically spaced baiiles through which vapor asments in the first of which molten zinc metal puricends and molten metal descends in tortuous or fied with respect to cadmium is obtained and dezig-zag paths.

livered to the second rectification treatment from The upper portion of the cadmium column is which zinc vapor purified with respect to lead built up of superposed rectangular trays 20 of 45 is obtained. The purified zinc vapor may be disilicon carbide or the like, with the top and botrectly burned for the production of zinc oxide, tom edges bevelled as in the case of the trays or may be condensed as Zinc dust, or utilized in 13, and the joints between trays made zincany other desired manner. vapor-tight with cement. 'Ihe bottom of each The invention may be carried out in various tray 20 has a transverse opening 21 approximate 50 forms and types of apparatus. We have illusone endthereof, and its upper surface is provided trated in the accompanying drawings an apwith spaced transverse ribs 22 parallel to the paratus particularly adapted for the practice of opening 21, the ribs being of progressively inthe invention. In the drawings creasing height from the end nearest the open- 05 Fig. 1 is a sectional elevation of the apparatus, ing to the end furthest therefrom. The trays 20 65 l to the openings2l (see Fig. 3).

are stacked in staggered relationship with respect Above the furnace structure 10, the column of trays 20 is surrounded by an appropriate layer of insulating material 23.

The bottom of the lowermost tray 20 approaches very close to the bottom of the uppermost tray 13, and the space between these trays available for vapor flow is consequently relatively narrow. For this reason the opening 21 in the lowermost tray 20 is directly above the opening 18 in the uppermost tray 13, so that vapor can ascend directly through these two openings. The inner. edge of the opening 21 has an upstanding rib or lip 29 terminating short of the sides of the tray-to direct molten metal overowng the tray into the troughs of the tray beneath, as more fully explained in connection with the similar arrangement illustrated in Fig. 5.

The cadmium column is surmounted by a condenser or dephlegmator 24. The amount of condensation in the dephlegmator is controlled by heat insulation in appropriate amount. Molten metal condensing in the dephlegmator flows back into the cadmium column by passing under a curtain wall 25 and over a dam 26. The curtain wall 25 acts as a skimmer to prevent any cadmium-rich zinc dust that may be formed in the dephlegmator from entering the cadmium column. Floating metallic dust is removed from time to time through a normally plugged tap hole'27 in the wall of the dephlegmator. A vapor outlet 28 communicates with the top of the dephlegmator.

Impure molten zinc metal is introduced into the cadmium column through a pipe 3()v communicating with a charging well 31. A continuous stream of molten metal flows into the charging well 31 through an opening 32 in the bottom, of a superposed charging well 33. The amount of molten metal owing through the opening 32 is regulated by adjustment of the position of a cooperating adjustable valve stem A34. An appropriate level of molten metal is continuously maintained in the upper charging well 33. The pipe 30 conveys the molten metal from the charging well 31 into one of the lower trays 20 of the cadmium column.

The bottom of the cadmium column is formed bya tray 35 having a lateral opening communieating with a discharge pipe 36. Molten metal is discharged from the base of the cadmium column through a liquid seal established by a partition wall 37, and is conveyed through the tube 36 to the lead-eliminating rectifying vcolumn (hereinafter designated lead-column).

The lower portion of the lead column is built within the heating chamber 41 of a furnace structure 40. The heating chamber is provided with burner openings 42 and an outlet 39 for the exhaust heating gases (see Fig. 4). This lower portion of the lead column is built up of trays 44 similar to the trays 14, and the upper portion of the lead column is built up of trays 50 similar to the trays 20. Molten metal is withdrawn from the base of the lead column through a discharge outlet 49. Above the furnace structure 40, the column of trays 50 is surrounded by an appropriate layer of heat insulating material 43.

The top of the lead column is connectedby an orice 45 with a zinc oxide combustion chamber 46. The combustion chamber is provided with ports 47 for the entrance of air. The zinc oxide fume produced by combustion of the zinc vapor in the chamber 46 is carried Oi thrOugh a pipe line 48 to an appropriate zinc oxide collecting device, such for example as a bag house.

Fig. illustrates the connection between the uppermost channeled tray 44.and the lowermost flat-bottomed tray 50. In consequence o! the form of these trays, the flat bottom of the lowermost tray 50 approaches very close to the at portion of the bottom of the uppermost chan- Vneled tray 44. Accordingly, the space available for vapor flow between these trays is so constricted as to possibly interfere with the free flow of vapor upwardly through the column. To obviate this difficulty, the opening 51 in the lowermost tray 50 is positioned directly above the opening 52 in the uppermost tray 44. Zinc vapor can thus ascend directly through these two registering openings without passing through the narrow space between the trays. In order to prevent short-circuiting of descending molten metal through these registering openings, the inner edge of the opening 51'of the lower-most tray 50 is provided with an upstandng rib 53 terminating short of each side oi the tray, thereby providing openings 54 so positioned that molten metal overowing the tray is directed into the side channels 55 of the uppermost tray 44 (see Fig. 5). As previously mentioned, a similar arrangement is provided between the correspondin g trays in the cadmium column.

In practicing the method of the invention in the apparatus illustrated in the drawing, a continuous stream of molten zinc metal contaminated with lead and cadmium flows through the pipe 30 into one of the trays 20 of the cadmium column. Heat is supplied in controlled amount to the lower portion of the column (by the heating chamber 11) to volatilize the molten metal in amount suiicient to rectify continuously the mixture of zinc and cadmium undergoing the rectiflcation treatment in the column. Metallic vapor ascends the column in intimate contact with the descending molten metal. In consequence of the rectifying action of the column, the ascending vapor becomes progressively enriched in cadmium and the descending (reuxing) molten metal becomes progressively freed of cadmium. A cadmium rich zinc vapor escapes from the top of the column into the dephlegmator 24. All but a cadmium-rich fraction of the vapor entering the dephlegmator is condensed therein and is returned to the rectifylng column for the further removal of cadmium therefrom. .The cadmium-rich fraction of the vapor uncondensed in thedephlegmator escapes through the pipe 28 to an appropriate recovery device (not shown), such as a canister, condenser, combustion chamber or the like.

Molten zinc metal, purified with respect to cadmium, accumulates in a. sump at the base of the cadmium column, and flowing under the curtain walll 37 is delivered by the ,pipe 36 to the lead column. The wall 37 provides a liquid seal for the discharge of molten metal from the cadmium column\into-tllead column. This liquid seal is necessary in order to prevent short-circuiting of cadmium-rich vapor into the lead column. It such vapor should enter the lead column, the cadmium therein would accompany and contaminate the puried zinc vapor delivered from the lead column to the zinc oxide combustion chamber.

The pipe 36 delivers molten zinc metal (puriiled with respect tocadmium) into one of the trays 50 of the lead column in a substantially continuous stream. "The lower portion of the lead column is operated in eiect as a zinc distilling retort or boiler, 'being adequately heated for this purpose by the hot gases flowing through the heating chamber 41. Metallic vapor ascencls the column in intimate contact with descending molten metal. In consequence of the rectifying action of the column, the ascending vapor becomes progressively freed of lead while the descending molten metal becomes progressively enriched in lead. The purified zinc vapor passes from the top of the lead column through the orifice 45 into the combustion chamber 46 where it is oxidized or burned in the presence of air to zinc oxide. The molten metal accumulating at the base of the lead column is high in lead and iron and other impurities with boiling points higher than that of zinc. This impure molten metal is tapped out of the column, either continuously or periodically, through the discharge outlet 49.

While molten metal is discharged from the base of both the cadmium column and the lead column, the lower heated portions of the two columns are operated in diii'erent manners. molten metal discharged from the bottom of the cadmium column consists of zinc contaminated with lead but purilied with respect to cadmium. Heat is supplied to the lower portion of the cadmium column in adequate amount to eiect continuous rectication of the mixture of zinc and cadmium undergoing treatment in the column. In other words, the base of the cadmium column is not heated with the object of driving oil' all of the zinc that enters it as vapor. hand, the molten metal delivered at the base of the lead column consists of lead, iron and other impurities with vboiling points higher than zinc accompanied by a limited amount of zinc. The purpose in heating the lower portion of the lead column is thus to volatilize as far as practicable all of the zinc that enters it and to deliver the resulting vapor in purified form to the zinc oxide combustion chamber after the vapor has passed through the rectifying column. 'I'he lower portion of the lead column is thus operate l in effect as a retort or boiler for distilling zinc metal.

While we have hereinbefore specifically described the utilization of the purified zinc vapor in the manufacture of zinc oxide, it is to be understood that the purified zinc vapor may be utilized in any other desired manner, as for example, in the manufacture of zinc dust.

The apparatus illustrated in the drawings as particularly adapted for the practice of the invention may be variously modifledjn construction and arrangement of operating units without departing from the principles of the invention. In general, the improved apparatus of the invention comprises a cadmium-eliminating rectifying column operatively associated with a leadeliminating rectifying column so that molten zinc metal purified with respect to cadmium is delivered from the base oi' the cadmium column to the lead column from which a puried zinc vapor is withdrawn. Various other forms of trans- The' On the other' verse bafes may be used in place of the trays illustrated in the drawings. When so available the impure zinc contaminated with lead and cadmium may be introduced into the cadmium column in the form of impure vapor rather than impure molten metal. Likewise, cadmium-rich metal may be withdrawn from the dephlegmator at the top of the cadmium column in the form of molten metal instead of vapor.

We claim:

1. The method of producing puried zinc vapor substantially free from cadmium and lead, which comprises introducing molten zinc contaminated with cadmium and lead into a cadmium-eliminating rectifying column, heating said molten zinc within the cadmium-eliminating column by conduction through a wall of the lower portion thereof to vaporize the molten metal at least in part, passing the resulting metal vapor in a substantially undiluted condition in contact with reuxing molten metal within the cadmiumeliminating column, withdrawing cadmium from the top of the cadmium-eliminating column, flowing reuxed molten zinc substantially free of cadmium but contaminated with the lead from the base of the cadmium-eliminating column through a molten metal seal into a lead-eliminating-rectifying column, heating the metal within the lead-eliminating column by conduction through a wall of the lower portion thereof to vaporize the zinc in large part, passing the resulting metal vapor in a substantially undiluted condition in contact with refluxing molten zinc within the lead-eliminating column, withdrawing lead from the base of the lead-eliminating column, and withdrawing zinc vapor substantially free from lead and cadmium from the top of the lead-eliminating column.

2. An apparatus for producing zinc vapor substantially free from cadmium and lead, which comprises a cadmium-eliminating rectifying column, means for introducing zinc contaminated with cadmium and lead into the cadmium-eliminating column', a heating chamber adjacent the lower wall portion of the cadmium-eliminating column, means for withdrawing cadmium from the top of the cadmium-eliminating column, a lead-eliminating rectifying column, a conduit connecting the base of the cadmium-eliminating column with the lead-eliminating column, a molten metal seal disposed between the cadmiumeliminating and the lead-eliminating column, a heating chamber adjacent a lower wall portion of the lead-eliminating column, means for withdrawing lead from the base of the lead-eliminating column, and means for withdrawing zinc vapor substantially free from cadmium and lead from the upper end of the lead-eliminating column.

PHILIP MCLEAN GINDER. WILLIS MCGERALD PEIRCE. ROBERT KERR WARING. 

